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Food Chains and Food Webs

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To define and discuss food chains and food webs. To discuss the concept of trophic levels. Finally, to evaluate the role of decomposers in food chains and food webs.

Hello everyone, welcome to the video tutorial for food chains and food webs. Today we are going to define what a food chain is and what a food web is. We will also discuss what a trophic level is, and it relates to food chains and food webs. Finally we will evaluate decomposers, and the role they play in a food chain.

Great, lets begin today’s tutorial by taking a look at a grassland ecosystem.

Sunlight provides energy to plant species, allowing them to carry out photosynthesis and produce sugars. These sugars can be used to meet energy demands within the plant or create new biomass. Within this ecosystem, an organism like this grasshopper will consume plant material to meet its metabolic needs. This grasshopper in turn will provide energy and nutrients to a predator such as this lizard, which in turn will become prey for another organism in the grassland ecosystem, like this hawk. Together these linkages, through diet and predation, make up one food chain.

A food chain represents the relationships between select organisms within one ecosystem based upon a hierarchy of their diet and consumption of one another. They are often used to visualize or pictorially represent the flow of energy, matter, and toxins between organisms through predator-prey relationships.

As there are more organisms in the grassland than just grasshoppers, lizards, and raptors, many food chains co-exist and overlap within any one ecosystem. The sum of all the predator prey relationships for an ecosystem is a Food Web.

Food webs are an integration of multiple food chains within one ecosystem. Ideally, a food web should contain all organisms present in an environment. This is rarely possible due to the immense number of microorganisms living in the soil, water and air, however the more organisms and linkages depicted, the more realistic the food web. Food webs are more dynamic than food chains as they also tend to include more detailed interactions between organisms.

Another important aspect of the food chains and food webs are trophic levels. A trophic level is a position in the food chain occupied by an organism based upon what it consumes, and what consume it.

The First level of any food chain is made up of primary producers. Plants often are used to represent this tier, however any autotrophic organism from the modeled ecosystem would fall in this category.

The Second level of a food chain is filled with primary consumers or herbivores. The term primary consumer is reflective of the energy source in the food chain. As the plants “fixed” the energy in chemical bonds within their organic matter, the first organism to consume plant matter is simply a primary consumer of that energy.

Predators occupy the third trophic level of a food chain; these organisms are sometimes described as secondary consumers, as they are the second organism in a food chain to receive energy initially derived from primary producers. These predators are not necessarily strictly carnivorous, as for example bears and human beings are both top-level predators that are omnivorous, consuming both plants and animals to meet nutritional needs.

Depending on the complexity of the ecosystem, there may be no trophic levels above secondary consumers, or there may be several. Regardless, every food chain ends with an Apex predator, the organism at the top of a food chain for that ecosystem, defined by having no natural predators above it. Apex predators play an important role in their ecosystem by regulating the flow of energy through the food web from the top down. However there is one more section of the food chain, that I have not mentioned, that is incredibly important to the function of the ecosystem. Decomposers!

This means that all of the organisms present in this foodweb will be processed by decomposers at one point or another. This also means that all food chains, and food webs truly end with decomposers.

Decomposers naturally play several important roles for the environment.

To begin, decomposers remove dead organic matter from the environment. Without decomposers, dead organic matter like animal wastes would continue to be present in the environment and pile up year after year. That’s a lot of waste.

Decomposers recycle important nutrients such as nitrogen and phosphorous that would otherwise be tied up in dead organic matter. Nitrogen and phosphorous are important for plant growth, and as plants are often the foundation of a food web, this nutrient recycling can ensure high productivity in the environment.

Some decomposers are also capable of breaking down complex woody C3 plant material such as lignin and tannin polymers. While it may take decades, or even centuries to decompose them completely, these are the only species on the planet capable of breaking down these structural plant products.

All food webs end with decomposers and yet decomposers promote growth for primary producers, enabling healthy food webs to continue.

To recap what we have covered: Food chains and food webs both are comprised of a series of linkages of predator prey relationships between organisms in an environment, based upon a hierarchy of who eats who. Food webs contain multiple food chains that coexist and often overlap. Trophic levels are positions within a food chain, occupied by organisms based upon what they eat, and how far removed they are from a primary source of energy. Lastly, all food chains and food webs end with decomposers, who recycle dead organic matter and nutrients back to primary producers.

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